Trucks such as dump trucks have commonly been used to convey materials such as salt, dirt, gravel and/or sand for the purposes of spreading these materials onto road surfaces to improve the traction of the road surface during hazardous driving conditions. Dump trucks have also been used to carry and dispense asphalt on road surface for road repair and maintenance. The materials in the truck are commonly dispensed by tilting the dump body of the truck thereby releasing the materials from the dump body and/or conveying the materials within the dump body out through an opening in the rear of the dump body. Dump trucks with integrated conveyance systems are illustrated in U.S. Pat. Nos. RE 25,709; 4,886,214; 4,266,731 and 5,397,172. These patents illustrate the common prior art methods for controlling the flow rate of material moved out of the dump body of a truck by an integrated conveyor. U.S. Pat. No. RE 25,709 illustrates the use of a slidable door and a rotatable feedgate to control the particulate flowrate from a conveyor. The slidable door similar in design to the slidable door illustrated in U.S. Pat. Nos. 4,886,214 and 4,266,731.
The sidable door is moved vertically and downwardly to control the flowrate of particulate material conveyed through the rear opening of a tailgate. The rotatable feedgate rotates about a fixed axis. The rotatable feedgate is rotated into the truck body to control the rate of discharge of material. Dump bodies used for bulk material such as asphalt and/or salt have had tailgates with openings which include rotatable feedgates or sidable doors, such as shown to U.S. Pat. No. RE 25,709. The rotatable feedgate and slidable door designs have been used for many years to control particulate flow rates from an integrated conveyor system mounted in the body of a dump truck. The slidable door disclosed in U.S. Pat. No. 5,397,172 is incorporated in a separate structure, called a hood and described in U.S. Pat. No. 4,886,214. The hood is designed to slidably shift between a forward and rearward position on the hood. The rearward shifting of the hood allows the truck to be used in the open hauling mode. Rotatable feedgates and slidable doors have long been used in combination with particulate conveying systems and rear spreaders to improve the particulate flow rate and dispersement by the conveyor from the rear of a dump truck.
Although prior spreading systems have improved the control of the flowrate of the dispensed materials from the dump body, these prior spreader systems are still inadequate for reliably controlling particulate flowrates over an extended period of time. Spreader systems which incorporate a slidable door such as shown in U.S. Pat. No. 4,886,214 are highly susceptible to jamming during operation. Slidable doors are guided by slots which maintain the door in position. These slots typically fill up with particulate material which passes through the tailgate door. Particulate material such as gravel and salt commonly gets lodged in the slots thereby preventing the slidable door from moving. Consequently, proper flow rate control of such particulate material is impaired. Dispensement of asphalt from a tailgate having a sidable door is even more problematic. Asphalt which becomes lodged in the door slots will eventually to bond the slidable door and to the slots thereby preventing further operation of the slidable door. The slots are also very susceptible to damage. The slots, over time, will deform in shape due to being bumped into by other objects, bend during operation, and/or rusting. Deformation of the slots results in impaired operation of the sidable door and ineffective control of particulate material flowrates. Rotatable feedgate designs overcome the jamming problems associated with slidable doors. Rotatable feedgates pivot about a single axis thereby essentially eliminating problems of jamming the feedgate when dispensing materials such as salt, gravel, asphalt, etc. Furthermore, the rotatable feedgate design is typically a more durable design thus less susceptible to damage during operation and daily use. However, when using a tailgate having a rotatable feedgate, low flowrate control of particulate material through the feedgate is difficult and unreliable. Due to the design of the rotatable feedgate, the opening of the rotatable feedgate allows particulate material to enter the feedgate from both the front and sides of the feedgate. The sidable door design only allows particulate material to pass through the front of the feedgate thereby providing better flowrate control of materials through the feedgate opening than rotatable feedgates, especially at low flowrates.
In the prior co-pending application, there did not exist a mechanism for actually controlling the size of the passageway while controlling side flow of a rotatable feedgate. Co-pending application Ser. No. 524,492 filed May 26, 1995 significantly improved the control of dispensing materials from a dump body, especially at low flow rates. The feedgate design overcame the problems of jamming and susceptibility to damage commonly associated with slidable door designs and further resolved the problem with the control of low particulate material flowrate associated with rotatable feedgates. The rotatable feedgate design was versatile enough to be used in a manual or automatic mode of operation and had a relatively simple and durable design. The rotatable feedgate could also be used in an open mode of operation for hauling long materials such as trees. In the open mode of operation, the rotatable feedgate was moved into the completely open position to rotate the rotatable feedgate into and behind the inner surface of the tailgate when the tailgate was opened to the laid open position. This position allowed objects to be laid over the tailgate opening during hauling. However, the versatility of the tailgate design was limited in the open mode of operation since the rotatable feedgate in the open position did not block the tailgate opening. As a result, objects being loaded and unloaded from the dump body could lodge themselves in the tailgate opening thus making the task of loading and unloading more difficult. In addition, the rotatable feedgate, in the open position, could not be used for open mode dumping or be used as a platform for dirt, sand, mulch, gravel, etc. The rotatable feedgate design of the prior co-pending invention was not compatible for using the tailgate in these operations since particulate materials could freely fall through the tailgate opening when the rotatable feedgate was in the open position. When the rotatable feedgate was in the closed position, the rotatable feedgate created an inconvenient obstruction extending upwardly from the inner surface of the tailgate thus making the rotatable feedgate essentially incompatible or inconvenient for use in these operations. As a result, there remains a demand for a truck body with a tailgate mounted flow control mechanism having the advantages of a rotatable feedgate which will allow the truck body to be used effectively in the tailgate down position. The prior co-pending application could not accomplish this function because of the inherent operation of a rotatable feedgate.